Why do things float in the water?

Bex Spiller May 2, 2018

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Let’s be honest, most of us love nothing more than a good ol’ bath. Of course, there are some people who swear by a shower rather than a bath – but whatever floats your boat. Talking of floating boats, have you ever wondered why things float in water? Perhaps you’ve always wondered why your favorite rubber ducky floats alongside you when you’re creating the ultimate bubble beard in the bath, or perhaps you’ve wondered why your favorite laptop didn’t float when you accidentally dropped it in the tub (not on purpose, may we add). Yep, if you want answers to all of those questions, check out the ultimate answer for why things float in the water…

It’s all about density…

If you don’t quite remember your high school physics lessons, you may have heard of the word ‘density’ in your adult life – although we have a feeling if someone said that word in relation to you and your intelligence, it wasn’t a compliment. Sorry. Yet, density plays a huge part in the question of whether an object will sink, or whether it will float. Every single object around the world is made up of molecules. Although you can’t see them with the naked eye, there are millions of these little guys in your food, your chair, your drinking glass and more – and it differs from object to object. Those that are denser (such as a rock) have lots of molecules all tightly packed together, while those that are less dense (like wood) have fewer molecules that are more spread out. If an object is less dense than water, they will be able to float. If they are more dense than water, they will sink! However, density isn’t all about weight. Although a cargo ship is made up of extremely heavy materials, these materials are filled with a lot of hollow space that is filled with air. This means it is less dense and can float easily.

….But also about buoyancy

While density is a huge part of whether an object floats or not, buoyancy also plays a role in this. This is caused by the surface of the object, and how much of it touches the water. Because of a cool thing called displacement, objects float because water pushes on the object that is trying to push water out of the way. It’s really like a game of tug of war! If more of the surface area is touching the water and pushing it away, even more of the water will push back, allowing them to equal out and result in the object floating on the water. If there is only a small surface, less of the object is pushing against the water, meaning that the water will win and the object will sink.

Doing it yourself

A great way to test both density and buoyancy yourself is to run yourself a nice bath and test out various objects around your house. You can see if heavier items with large surfaces can float, and you can see if lighter items with smaller surfaces can float. By looking at the objects, their weight, their size, their surface area, and what kind of material they are made out of, you should be able to make an educated guess about whether it will float or sink, before trying it out for yourself!

Most of us can’t go a day without seeing something float. It may be a boat in the ocean, it may be a sponge in your kitchen sink, or it may just be a rubber duck in your bath. But did you ever know why things float?